Please help ASAP! Need this for a test! Find the constant of proportionality (r) in the equation y = rx

At the beginning of 1974/75,2 years a man invested #2000 in a bank at 12.5% compound interest, if it degree #650 at the end of each two years to pay his son's school fees, after payment of interest to pay his son's school fees, how much did he have left at the beginning of the 1978/79 school year?

3x = 729 solve for x plz . it's urgent. will mark

In the diagram, ab is tangent to c, ab = 4 inches, and ad = 2 inches. find the radius of the circle.